Hot melt extrusion apparatus

ABSTRACT

An apparatus and method for applying hot melt coatings to the under face of a web from the orifice of a coating head. The extrusion pressure preferably lifts the web slightly by overcoming web tension. Uniform heat is achieved by central feed to the head. Smoothing doctor blades are not required and the head is movable relative to a fixed back-up roll so that roll readjustment is not required when rethreading. One extrusion lip is flexible and independently movable relative to the other to permit change in width of the elongated extrusion orifice. A relatively light, distortable lip bearing member is provided.

United States Patent 1191 Herzog 1 51 Nov. 18, 1975 1 1 HOT MELTEXTRUSION APPARATUS [75] Inventor: Peter Herzog, Chemin du Martinet,

[2]] Appl. No.: 414,519

[52] US. Cl. 118/410; 118/253; 118/419 [51] Int. Cl? B05C 3/12 [58]Field of Search 118/410, 424, 419, 429,

Dentch et al. 118/410 Heijnis et a1. 118/410 Primary Examiner-W. C.Reynolds Assistant ExaminerDoug1as Salser Attorney, Agent, orFirmPearson & Pearson [57] ABSTRACT An apparatus and method for applyinghot melt coatings to the under face of a web from the orifice of acoating head. The extrusion pressure preferably lifts the web slightlyby overcoming web tension. Uniform heat is achieved by central feed tothe head. Smoothing doctor blades are not required and the head ismovable relative to a fixed back-up roll so that roll readjustment isnot required when rethreading. One ex- 56 References Cited I UNITEDSTATES PATENTS trusion lip is flexible and independently movablerelative to the other to permit change in width of the elon- SEI P gatedextrusion orifice. A relatively light, distortable een i 3,348,52610/1967 Ncubaucr i 1 18/410 hp bearmg member 18 provlded' 3,556,8321/1971 Park 118/410 1 Claim, 4 Drawing Figures l 2 lo I'- L 3O 3O 22 US.Patent Nov. 18, 1975 Sheet10f2 3,919,974

I g) Q52 US. Patent Nov. 18, 1975 Sheet 2 of2 3,919,974

HOT MELT EXTRUSION APPARATUS BACKGROUND OF THE INVENTION U.S. Pat. No.2,464,771 of Mar. 15, 1949, to Van Guelpen discloses an angularlytiltable extrusion head over which a web under tension is passed forcoating the under, face, but no backer roll is used opposite the orificeand a doctor, or smoothing, blade is in rear of the orifice along theweb path to actually produce the smooth coating. Such a device is notlikely to produce a commercially acceptable, thin, low cost coating fromviscous, tacky, hot melt substances which range from 5,000 to 500,000cps.

One solution to the problem of commercially successfully handling suchhot melt coatings at high line speeds and with desired uniformity isfound in U.S. Pat. No. 3,556,832 of Jan. 19, 1971 to Park. Apparatus isdisclosed in this patent wherein a web to be coated is passed over astationary, somewhat rounded coating head having an elongate slit. Papermoves over the elongate slit bearing against the rounded coating head.Hot melt material is extruded through the elongate slit onto the paper.An important part of this process is the transverse stretching of theweb as it approaches the coating head and the guiding of the web undertension into sliding contact with the coating head itself. The coatingprocess described by Park generally includes the steps of simultaneouslycontrolling the rate of flow of the coating material to exert a pressurethat is somewhat greater than an opposing force on the tension web, aforce normally achieved with a press roll.

In general, the process disclosed by Park has been a successful anddesirable commercial process.

Indeed the process has been found to be so broadly applicable that therehas been a need for improved apparatus that will permit fullexploitation of the process capabilities.

SUMMARY OF THE INVENTION Therefore, it is an object of the invention toprovide an improved extrusion head apparatus which can be used toachieve improved coating precision of hot melt materials and is readilycleaned and adjusted to meet various processing conditions.

It is a further object of the invention to provide apparatus which hasan improved self-cleaning characteristic during operation.

Another object of the invention is to provide a more efficient coatingapparatus, one characterized by a more dependable maintenance of webtension.

Other objects of the invention will be obvious to those skilled in theart on reading the instant application.

The above objects have been substantially achieved by constructing acoating apparatus comprising a coating head, or extrusion die, whereinthe web-support members forming an elongate slit comprise elongatelead-on members and lead-off members at least one of which is adjustablymounted for overall positioned adjustment with respect to the othermember and also for adjustment of slit width along the length of theslit by means of adjusting either compression or tension on individualadjusting means spaced along the member.

This adjusting feature, permitting as it does finer control over theslit width, also allows central feed to a plenum chamber from which theelongate slit feeds hot ILLUSTRATIVE EXAMPLE OF THE INVENTION In thisapplication and accompanying drawings there 0 is shown and described apreferred embodiment of the invention and suggested various alternativesand modifications thereof, but it is to be understood that these are notintended to be exhaustive and that other changes and modifications canbe made within the scope of the invention. These suggestions areselected and included for purposes of illustration in order that othersskilled in the art will more fully understand the invention and theprinciples thereof and will be able to modify it in a variety of forms,each as may be best suited in the condition of a particular case.

IN THE DRAWINGS FIG. 1 is a partially diagrammatic section in elevationand showing the relationship of the apparatus of the invention to a webbeing coated therewith.

FIG. 2 is a section of the extrusion apparatus as defined by sectionline 2-2 on FIG. 4.

FIG.'3 is a section of the apparatus as defined by section line 33 onFIG. 4.

FIG. 4 is a sectional view of the coating apparatus of the inventiontaken through a plane which is normal to the direction of the web beingcoated.

Referring to FIG. 1, it is seen that coating apparatus 10 comprises acoating head 12 which is mounted for angular movement by an hydraulicram 14 by means of a bracket 16 mounted for skewed movement on shaft 18within arcuate slot 20.

A paper web 22 is passed left-to-right across coating head 12 andreceives a layer 24 of a hot melt barrier coating 26. g

A fixed press roll 28 is mounted on the opposite side of web 22 andforms means to support said web against pressure exerted by coatingmaterial being forced under pressure onto the web from coating head 12.Idler rolls 30 form means to keep web 22 in snug contact with coatinghead 12.

FIGS. 3 and 4 show details of coating head 12. The coating head isformed of a primary housing which encloses a plenum, or manifold chamber32. Coating material is forced into this chamber through a conduit 34and thence through an elongate slit 36 onto the web to be coated. Slit36 is formed of two elongate members, each of which comprises aweb-contacting surface, one of which we shall refer to as lead-onsurface 38, the other as lead-off surface 40. Lead-on surface 38 formsthe web supporting surface of static lead-on member 42. Lead-off surface40 forms the web-supporting surface of the static lead-off member 44.

Lead-on member 42 is fixed by bolt 46 to the housing of plenum chamber32. However, lead-off member 44 is not so attached.

Lead-off member 44 is mounted for adjustment of its position withrespect to member 42 by means of a series of spaced threaded fasteners48 which form means to push or pull member 44 as is required to adjustthe width of slit 36. Member 44 is sufficiently distortable along itslength that fasteners 48 can be utilized to, for example, make theextreme ends of slit 36 wider than the center thereof, or make whateverother modification in slit width is made desirable along the lengththereof.

Fasteners 48 are held in a support plate 50 which in turn is fastened toplenum chamber housing 51 by fasteners 52. A clamp plate 54 is utilizedto hold member 44 snugly against housing 51 with bolts 55.

FIG. 2 shows end plates 56 which are fastened by bolts 58 to housing 51and thereby form the lateral walls of plenum chamber 32.

More detail of the apparatus is shown in H0. 4. Press roll 28 isequipped with ports 60 and a chamber 62 for accommodating heating orcooling fluids as may be required for a given coating operation.

Unlike prior art coaters, the press, or backing, roll 28 is rotatable infixed bearings 64 and 66 in frame 68. Thus the web path and web tensionremain constant and are not affected by any displacement of the roll.Because the roll cannot be elevated, flying splice operation isfacilitated. The backing roll 28 is not subject to skewing, becauseskewing is accomplished with the adjustable movable coating head 12. Forthreading of the web, the coating head may be tilted and compensationmay be made for non-parallelism by skewing the coating head in ahorizontal plane.

The center feed to the plenum 51 assures uniformity of distribution ofcoating to both ends of the extrusion slot. It should be noted thatthere are no gap adjusting screws which cross the extrusion slot tointerfere with flow, adjustment of slot opening being accomplished byscrews exterior to the slot and outside the coating path.

While the device of the above mentioned Van Guelpen patent relies on adoctor, or smoothing, blade for achieving a thin, smooth, uniformcoating of tacky, viscous hot melt substance, the device of thisinvention achieves a commercially acceptable coating by properadjustment of the width of the slit, or orifice, 36, together withangular adjustment of the coating head to the web and to the fixedbacking, or press roll 28.

The extrusion orifice, slit or nozzle 36 of the apparatus of thisinvention may also be used to extrude' cold viscous material whichincludes a predetermined percentage of solvents, such as dispersions,lacquers (nytro-lacquers) and rubber cements with benzine solvents. Highviscosity materials of many types may be applied in thinner thanconventional layers to thereby save considerable drying time. Capitaloutlay for drying equipment, such as heat tunnels, ovens and the like,and the floor space for coating apparatus is thus greatly reduced.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed and all statements of the scope of the invention which mightbe said to fall therebetween.

I claim:

1. Apparatus for coating the underside of a web advancing at apredetermined rate along a generally horizontal path, said apparatuscomprising:

a press roll mounted at each opposite end in fixed bearings to extendtransversely of said web above said path for guiding and supporting saidweb in an unchanging said path during splicing thereof;

coating head means, mounted at each opposite end in support pivots, toextend transversely of said web under said path, for forming a coatingnip therewith, said means including actuating mechanism forindependently pivoting one said end relative to the other to skew saidhead relative to said roll to control coating thickness,

said coating head having an elongated lead-on lip and an elongated,rounded, lead-off lip removably mounted thereon and jointly defining anarrow extrusion slot connecting with a central feed plenum chamber,said slit and chamber being free of obstructions and free of gapadjustment screws in the path of extrudate emerging from said slit;

said lead-off lip being flexible and distortable along its length andsaid head including a plurality of spaced threaded screws therealongforming means to push and pull said lead-off lip to vary the width ofsaid slit and control the thickness of coating extruded therefrom.

1. Apparatus for coating the underside of a web advancing at apredetermined rate along a generally horizontal path, said apparatuscomprising: a press roll mounted at each opposite end in fixed bearingsto extend transversely of said web above said path for guiding andsupporting said web in an unchanging said path during splicing thereof;coating head means, mounted at each opposite end in support pivots, toextend transversely of said web under said path, for forming a coatingnip therewith, said means including actuating mechanism forindependently pivoting one said end relative to the other to skew saidhead relative to said roll to control coating thickness, said coatinghead having an elongated lead-on lip and an elongated, rounded, lead-offlip removably mounted thereon and jointly defining a narrow extrusionslot connecting with a central feed plenum chamber, said slit andchamber being free of obstructions and free of gap adjustment screws inthe path of extrudate emerging from said slit; said lead-off lip beingflexible and distortable along its length and said head including aplurality of spaced threaded screws therealong forming means to push andpull said lead-off lip to vary the width of said slit and control thethickness of coating extruded therefrom.